Hermetically sealed waveguide window with non-sputtering iris



Aug.v20, 1963 R. M. WALKER ETAL HERMETICALLY SEALED WAVEGUIDE WINDOW WITH NON-SPUTTERING IRIS Filed May '7, 1957 G08 F/ZLED SECTION d Z M i p 3% 4mm"- rates The present invention relates to wave guide windows for controlling the wave propagation as well as for establishing a high vacuum seal between two wave guide sections.

atent 1 It is one of the principal objects of the invention to provide a window of the above indicated nature which allows practically reflectionless transmission of electromagnetic waves of a predetermined frequency through Waves guides or other transmission lines requiring therewith a hermetic, high vacuum-type seal.

Other objects are to provide a hermetically sealed iris construction which is especially suited for transmit-receive (TR) and anti-transmit-receive (ATR) tubes making it possible to achieve with such tubes performance characteristics heretofore considered impossible, to provide a mechanically effective sealing means whose geometry is not limited by the electrically effective configuration of an iris, the latter being not restricted to shapes and sizes that are compatible with the strain characteristics of the sealing component, to provide a wave guide window construction of the above type which is particularly advantageous for the designing of so-called resonant windows giving access to broad bnand TR and ATR tubes, to provide a hermetically sealing iris structure which achieves particularly lowlinsertion and are losses by eliminating sputtering across the, iris thus avoiding the formation of a film across the sealing dielectric which film increases the insertion and arc losses, and generally speaking to provide a device of this type which has essentially improved reproducibility and design flexibility.

A brief summary of the invention will serve to indicate various aspects of its nature and substance for accomplishing the above objects, as follows.

In one aspect, a window device for the controlled propagation of electromagnetic energy in Wave guides or other transmission lines comprises, in combination with a wave guide portion, the following elements:

A metallic iris component which fits the guide portion and has a wave controlling opening of any desirable configuration; a sealing component located adjacent to the iris component at a predetermined distance therefrom and including a dielectric window portion having around its entire periphery, where it fits the guide portion, a metallic frame portion; and between the guide portion and the frame portion of the sealing component a metallic seal (such as solder) in gas tight cohesive contact with the guide portion as well as the frame portion. In most instances it is preferable to arrange the iris component within the evacuated wave guide section. At any rate, the sealing and wave control functions can be strictly separated.

In another aspect, the invention involves the com-bination within a wave guide of a sealing component which has a metal frame port-ion and of an iris component, both components fitting the guide and being arranged side-byside therein, the dimensions of the iris opening and the opening of the metal frame portion of the sealing component being coordinated in such a manner that resonance results at a predetermined separation of the two openings.

In a preferred embodiment, the hermetic seal is provided by a metallic such as soldered, brazed, or welded joint between the metallic frame of the sealing component and the wave guide proper, the sealing metal flowing into 3"]:0]. Patented Aug. 20, 1963 ice thecentral part of the dielectric plate, forming iris openings of predetermined dimensions and configurations for the above-mentioned cooperation with the opening of the iris component, as affected by the distances of the several openings. The distance between the sealing and iris components can be exactly predetermined for example by dishing an iris plate, or by similarly dishing the sealing plate if it has a solidly metallic frame portion or, if both plates are essentially flat, by providing a spacer therebetween.

In a further aspect, iris openings are formed at both, sealing and iris components, and used at a separation proper for providing a predetermined resonant condition rather than for cancellation of reflections from one by the other; both sealing and iris elements can be made resonant independently or together, or both elements may be non-resonant at a desired frequency but compensating to provide the desired resonant frequency for the dual unit.

In an additional aspect, different metals are used for iris and sealing components, respectively, in order to obtain specific characteristics not otherwise obtainable.

These and other objects and aspects of the invention will appear from the following description of several typical embodiments illustrating its novel characteristics.

The descriptionrefers to a drawing in which FIG. 1 is the front elevation of a TR tube incorporating the invention;

FIG. 2 is a section on lines 22 of FIG. 1, with the electrodes in elevation;

FIG. 3 is a transverse section with the window in elevation, of a wave guide incorporating another embodiment of the invention;

FIG. 4 is a section, corresponding to FIG. 2, on lines 44 of FIG. 3;

FIGS. 5 and 6 are elevations of sealing components illustrating additional embodiments of the invention;

FIG. 7 is a section on lines 77 of FIG. 6;

FIGS. 8 and 9 are elevations of dished iris plates in accordance with the invent-ion; and

FIG. 10 is a side elevation indicating the shape of plates according to FIGS. 8 and 9.

FIGS. 1 and 2 indicate at 21 a wave guide portion of a transmissionreflection tube which, :as well known, is highly evacuated and instead filled with gas of exactly predetermined composition and pressure. 22 indicates the flange of the tube with the aid of which it can be joined to another wave guide section of the system. 23 and '24 are electrodes which are'kept at a predetermined potential difference, for purposes well known in the art but irrelevant to the present invention. A sealing component according to the invention is indicated at 25, and an iris component at 26, whereas the metallic seal is indicated at 28.

In the embodiment according to FIGS. 3 and 4, two wave guide portions 31.1 and 31.2. contain near their juncture a sealing window which comprises a sealing component 35, an iris component 36, aspacer 37 and a metal seal 38. If desired, the wave guide sections 31.1 and 31.2 may be joined by means Oif metal straps 3-2 extending over the entire joint of the wave guide sections.

sealing component is made according to FIGS. 5, 6, and 7 and consists of a blank 25.1 of glass or ceramic material of a thickness s1 which has a metallized frame portion 25.2, applied to the blank by conventional methods, such as by painting or printing with metallic, for example silver paint followed by baking, or by gun spraying, or by vacuum deposition; in either case the metal of the irame is in intimate molecularly cohesive contact with the glass or ceramic plate, forming an impenetrable juncture therewith. In the embodiment shown in FIGS. 1 and 2, the metallized frame 25.2 is restricted to the edge of the plate and serves only for providing a hermetic seal between the sealing plate and the wave guide, whereas in other embodiments the metallized frame can provide iris structures of selected dimensions and configurations, such as for example shown in FIGS. and 6 respectively. As indicated in FIG. 7, both sides of the metallized frame can be extended toward the center of the sealing plate 251 so that two distinct iris structures of diiferent or similar shape can be provided, the thickness of the plate 25.1 permitting the exact predetermination of the separation of two irises and the separation of one or two irises from the iris proper of the other component.

The sealing component according to FIGS. 3 and 4 is a conventional window, consisting of a glass portion 35.1 which is joined to the metallic frame portion 35.2 by means of a standard glass-to-metal seal, the metal being an iron-nickel-cobalt alloy and the glass being of the boron-silicate type.

As indicated at 23 of FIG. 2 and at 38 of FIG. 4, the sealing component is joined to the wave guide by means of a sealing metal such as soldering, brazing or welding metal which completely fills the space between the [frame portion 25.2 or 35.2 of the sealing plate and the wave guide 21 or 31.1 respectively, thus providing :a hermetically tight seal independently of the iris plate 26 or 36.

The iris component 26 according to FIGS. 1 and 2 is dish-shaped, providing a contact face 26.1 which determines the exaot spacing between the sealing plate and the iris plate as clearly indicated at s2 in FIG. 2. The iris plate may be of any thickness s3 and of any configuration that is practicable or desirable for electrical purposes.

The iris component 36 according to FIGS. 3 and 4 is flat as indicated in FIG. 4, and the distance between sealing plate and iris plate is determined by a spacer 37.

Although a complete seal is provided by the metal 28 or 38 between the guide and the sealing plate, this metal seal can be extended into the space between the guide and the iris plate.

As indicated at FIGS. 8 to 10, the opening 26.5 or 26.6 of the iris plate is of selected dimensions and configurations similarly to the opening of the sealing plate shown in FIGS. 5 to 7.

The iris plate is preferably arranged on the vacuum side of the sealing plate, as indicated in FIG. 2, for the reasons presently to be pointed out; however if the reverse order should be preferably in a given instance, various unique advantages of the invention such as the perfect seal and the availability of several ir-i-ses are still present.

In an actual embodiment according to FIGS. 1 to 4, incorporating a sealing plate as shown at 35 of FIG. 4 in combination with an aperture plate as shown at 26' of FIG. 2, the dimensions which are indicated in these figures were as follows:

The iris plate was made of stainless steel and the metal seal consisted of soft solder applied by means of a gasair torch.

4 Characteristic electric data indicating the quality of this construction are as follows:

Insertion loss .05 db. Arc loss .10 db. Bandwidth 15%. Peak power rating (kilowatts) 500 kw. Average power rating 500 watts. Frequency (kilomegacycles) 9 krnc.

After several hundred hours of operation no evidence of sputtering of the iris or film deposition on the dielectric seals could be detected Visually or by insertion loss measurements.

Conventional structures previously used for tubes of this general type at the same frequency exhibit the following characteristics which demonstrate the superiority of the present invention:

Insertion loss .25 db. Arc loss .25 db. Bandwidth 12%. Peak power rating (kilowatts) 200 kw. Average power rating 260 watts.

After operation for 100 hours or more, sputtering and film deposition on the dielectric seal is always visible when these previous structures are used.

The above figures show a considerable advancement in this art in the following aspects: (a) a reduction of insertion loss to /s of the former value; (b) a reduction of arc loss to /s of the former value; (c) an increase of Bandwidth of 3%; (d) an increase of Power Handling to 25 0% of its former value.

It has been proposed (compare for example U.S. Patent No. 2,407,069 of September 3, 1956 to Milan D. Fisk) to seal irises by means of fiat or bulbous dielectric bodies which do not fill the iris opening but are joined to the iris structure in some other manner. Such constructions however do not provide hard vacuum seals nor do they have the advantages of the present invention which are based on the strict separation of the sealing and iris func trons, namely lower insertion loss, lower arc loss, elimination of sputtering, and better reproducibility and design flexibility.

The insertion loss in a standard window (such as part 35 of FIG. 4 if it were used by itself without part 36) is inversely proportional to b'/b namely the heights of window and wave guide as marked in FIG. 3. The bandwidth of the unit is proportional to b'/b, and the arc loss is proportional to (b'/ [1)2. It can readily be seen that b'/b must be small for low arc loss and large for 10w insertion loss. In conventional TR tubes the bandwidth is usually adjusted to a value which is about 2 times that of the tuning elements of the tube in which the window is used. The value of b'/b for this condition is normally about A to /3 for tubes designed for a 12% bandwidth. The insertion .loss for standard windows in this b/b range is 3 to 5 times the loss in windows where b'/b is This loss is contributed by dielectric losses in the glass and heating losses in the metal. Therefore the design of a TR tube using the standard window represents a compromise between high power handling (low arc loss), desirable bandwidth and insertion loss. The insertion loss is reduced by increasing the separation between the dielectric and. the iris which decreases the field strength in the dielectric, and the dual element window according to the present invention therefore eliminates the requirement for the above-discussed compromisc. In such a window, b/b can be made A or larger in parts 25 or 35, thereby reducing the insertion loss by a factor of 3 to 5. The bandwidth and the arc loss are controlled independently by the dimensions of. parts 26 or 36 which can be made of any metal including those having high conductivity, or which can be plated with high conductivity materials, so that the insertion loss complex iris shapes such as shown in FIGS. 8 and 9.

This means that the are loss can be reduced by the present dual element window by a factor of 4 'or more as compared to the standard glass-metal seal type.

Window sputtering occurs in high power pulse operation where a high intensity discharge is maintained across the input window on the inside of the TR or ATR tube. This discharge presents a short circuit across the transmission line, thereby preventing high frequency energy from reaching the receiver. The intensity of the discharge is so great that localized heating occurs and chem?- ical action takes place between gas within the tube, vapors, and the metal. This phenomena causes erosion of the metal and sputtering of metallic particles across the opening. These particles form a metallic film across the glass of the conventional window or of the above-mentioned window with an incompletely separated sealing element. This causes the insertion loss to increase during tube life. The chemical reaction also changes the gas composition inside the tube until all of the water vapor has been converted to hydrogen and metallic oxides. Sputtering rates in metals vary a great deal and some are for this purpose much better than others, but the metals used for glass to metal sealing are particularly bad in-this respect. In the dual element windowaccording to the invention the discharge takes place within the opening in part 26 or 36 which can be made of any metal so thatthose having low sputtering rates can be employed.

The reproducibility and design flexibility of the window according to the invention are definitely more favorable than in the heretofore known glass to metal seal It should be understood that the present disclosure is for the purpose of. illustration only and that this inven tion includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

1. In waveguide apparatus, a sealing Window device comprising, in combination: a metallic waveguide portion made essentially of metal chosen for its electrical conductivity properties; a metallic iris component located within said waveguide portion and having awave controlling iris opening, said iris component being made essentially of a second different metal which substantially will not sputter onto dielectric window material in close proximity thereto in the presence of an electric discharge across said iris opening; a hermetic sealing component having dielectric window means framed in a frame metal chosen for its dielectric-to-metal scaling properties located adjacent the outer side of said iris component relative to the interior of said waveguide portion, the frame aperture of said frame metal being everywhere larger than said iris opening and non-resonant at the intended frequency of operation of said apparatus and located so that all points on the periphery of said iris opening confront substantially only the dielectric material of said window means, said dielectric window means and said iris component in the vicinity of said iris opening being both substantially planar and parallel to each other, one of said components being bent along a line substantially parallel to its periphery and having its periphery directed from said line toward the other element, said iris component and the frame metal of said sealing component being peripherally in contact with each other, said frame metal being hermetically sealed to said waveguide portion by a totally metallic seal, and said dielectric window means being located less than one-quarter wavelength in said waveguide portion of electromagnetic wave energy at said frequency of operation from said iris element.

2. Device according to claim 1 wherein said wave guide portion includes flange means at an end thereof and there forming an outwardly open recess, and wherein said iris and sealing components fit into said recess where constructions, because it is not necessarily dependent on 1 glass to metal seals with their well-known unavoidable variations in resonant frequency, are losses and insertion loss which are functions of technological factors such as sealing temperature, cleanliness of materials and surface roughness of the metal. Similar problems are introduced by the sealing cement and the spacers of the abovementioned previously suggested window with an incompletely separated sealing body. All this is avoided by the present window construction with itscornplete separation of the sealing function, with its metallic joint between sealing plate and wave guide, and with its avoidance, if desired (FIGS. 1, 2) of (any glass metal seal. If a sealing plate according to FIGS. 1 and 2 is used to supply an electrically eflective iris, the metal frame 25.2 of element 25 (FIGS. 1 and 2) which forms this iris can be arranged outside of the vacuum so that it is not subject to sputter- 'ing. The separation of the sealing and iris components said sealing means is in contact with said guide.

3. Device according to claim 1 wherein said guide portion has an internal peripheral recess for receiving 'said iris and sealing components.

4. Device according to claim 1 wherein at least the surface of said iris component consists of stainless steel, whereby metal sputtering onto the sealing component is essentially eliminated for the useful life of the device.

References Cited in the file of this patent UNITED STATES PATENTS 2,407,069 Fiske Sept. 3, 1946 2,422,189 Fiske June 17, 1947 2,567,701 Fiske Sept. 11, 1951 2,683,863 Curtis July '13, 1954 "2,817,823 Olcress Dec. 24, 1957 2,821,658 Niaugler Ian. 28, 1958 2,834,949 Duffy May 13, 1958 Y FOREIGN PATENTS 684,887 Great Britain Dec. 24, 1952 

1. IN WAVEGUIDE APPARATUS A SEALING WINDOW DEVICE COMPRISING, IN COMBINATION: A METALLIC WAVEGUIDE PORTION MADE ESSENTIALLY OF METAL CHOSEN FOR ITS ELECTRICAL CONDUCTIVITY PROPERTIES; A METALLIC IRIS COMPONENT LOCATED WITHIN SAID WAVEGUIDE PORTION AND HAVING A WAVE CONTROLLING IRIS OPENING, SAID IRIS COMPONENT BEING MADE ESSENTIALLY OF A SECOND DIFFERENT METAL WHICH SUBSTANTIALLY WILL NOT SPUTTER ONTO DIELECTRIC WINDOW MATERIAL IN CLOSE PROXIMITY THERETO IN THE PRESENCE OF AN ELECTRIC DISCHARGE ACROSS SAID IRIS OPENING; A HERMETIC SEALING COMPONENT HAVING DIELECTRIC WINDOW MEANS FRAMED IN A FRAME METAL CHOSEN FOR ITS DIELECTRIC-TO-METAL SEALING PROPERTIES LOCATED ADJACENT THE OUTER SIDE OF SAID IRIS COMPONENT RELATIVE TO THE INTERIOR OF SAID WAVEGUIDE PORTION, THE FRAME APERTURE OF SAID FRAME METAL BEING EVERYWHERE LARGER THAN SAID IRIS OPENING AND NON-RESONANT AT THE INTENDED FREQUENCY OF OPERATION OF SAID APPARATUS AND LOCATED SO THAT ALL POINTS ON THE PERIPHERY OF SAID IRIS OPENING CONFRONT SUBSTANTIALLY ONLY THE DIELECTRIC MATERIAL OF SAID WINDOW MEANS, SAID DIELECTRIC WINDOW MEANS AND SAID IRIS COMPONENT IN THE VICINITY OF SAID IRIS OPENING BEING BOTH SUBSTANTIALLY PLANAR AND PARALLEL TO EACH OTHER, ONE OF SAID COMPONENTS BEING BENT ALONG A LINE SUBSTANTIALLY PARALLEL TO ITS PERIPHERY AND HAVING ITS PERIPHERY DIRECTED FROM SAID LINE TOWARD THE OTHER ELEMENT, SAID IRIS COMPONENT AND THE FRAME METAL OF SAID SEALING COMPONENT BEING PERIPHERALLY IN CONTACT WITH EACH OTHER, SAID FRAME METAL BEING HERMETICALLY SEALED TO SAID WAVEGUIDE PORTION BY A TOTALLY METALLIC SEAL, AND SAID DIELECTRIC WINDOW MEANS BEING LOCATED LESS THAN ONE-QUARTER WAVELENGTH IN SAID WAVEGUIDE PORTION OF ELECTROMAGNETIC WAVE ENERGY AT SAID FREQUENCY OF OPERATION FROM SAID IRIS ELEMENT. 